Ch 16.1 Electric Charge and Static Electricity

• Electric charge:– Fundamental force of electromagnetism

… magnets make electricity and electricity can make a magnet

–We don’t know why…it just does…it’s one of 4 forces that “run” science:

gravity, em, strong and weak nuclear.– Can be positive or negative– Like charges repel (push away), opposite

charges attract

Electric charge• Where does the charge come

from?– Atoms have positive (protons in nucleus)

and negative parts (electrons in orbitals)– The electrons, because they are on the

outside of the atom, can move from one atom to another or even one object to another!

– e.g. balloon–Measured in Coulombs

Moving electrons• Three ways can move from 1

object to another– Friction: rub them off, e.g. balloon on

hair, feet on carpet– Contact: touching a charged object to a

non-charged one, e.g. sticking balloon to a wall, get zapped when touch metal

– Induction: bringing object close to non-charged, balloon and water.

Moving electrons• So…–When you rub a balloon on your head

(friction)• Electrons move from your hair to the balloon

and the balloon becomes negatively charged• Your hair becomes positively charged and

sticks up because those charges repel

– As the balloon gets closer to the wall (induction)• The wall’s electrons are repelled and the

surface becomes positively charged• The balloon sticks because opposite charges

attract

Moving electrons• Can also move within an single

object is a conductor.–Metals make good conductors because

they have lots of valence electrons to lose

• If the substance does not allow movement of charge, it is called an

insulator.– Nonmetals make good insulators

Electric Force• Those attractions and repulsions

are electrical forces• The amount of force between

two objects depends on:– Amount of charge (directly…more

charge = more force)– Distance between charges

(indirectly…more distance, less force)

Electric Force• Doesn’t have to be touching!• Electric force is a field force,

commonly drawn with lines going in to negative and out of positive